Starting Thursday, the manual search will involve a slide of the hand compared to the traditional pat down, NBC News has learned. TSA agents will use the front of their hands in searches, and the new process will include an agent running his or her hand up the inside of a passenger's leg.

TSA did not confirm details for security reasons, but did acknowledge a change in procedure.

"TSA is in the process of implementing an enhanced pat-down at security checkpoints as one of our many layers of security," said Luis Casanova, a TSA public affairs officer.

Pat downs are used on passengers who opt out of full-body scanner technology, as well as those that set off walk-through metal detectors or are selected for a random search.

Casanova said TSA constantly evaluates its security procedures. "Terrorism evolves. It's gone from hijacking planes to trying to blow them up in the air," he said.

Meanwhile, airport screening continues to evolve with the rollout of full-body image scanners. TSA on Thursday rolled out high-tech body scanners at Newark International Airport. The machine creates a computerized image of a person's body and give screeners the ability to check for weapons.

The scanners debuted at Kennedy Airport last week. As of Oct. 22, there are 317 machines in 65 airports across the country, Casanova said. TSA hopes to have 450 installed by the end of the year.

TSA officials will be at Newark Liberty Airport on Thursday to demonstrate the machines and procedures.

TSA says the technology is optional for all passengers.

Msnbc.com, NBC News and The Associated Press contributed to this report.